IntroductionLymph is the protein-rich fluid that flows through the lymphatic system and surrounds all tissues.
- Lymph flows through lymphatic vessels and lymph nodes and is part of the immune system that is responsible for removing foreign microbes to lymph nodes and returning proteins to the blood.
- Unlike blood, which flows around the body in a loop by force created by the pumping mechanism of the heart and calf muscle, lymph flows in only one direction.
- The direction of the lymph flow is controlled by one-way valves and the flow is controlled by intrinsic contractions of lymph collectors created by the activity muscles surrounding the vessels.
- Problems that lymph may cause are primarily because there is no pump in the system.
- Lymph fluid consists of proteins, water, cells (RBCs, WBCs, lymphocytes which help to fight infections in the body), waste products, and fat in the intestinal lymph. It carries about 75-100 grams of protein circulating in the body per day.
The anatomy of the lymphatic system closely parallels that of the peripheral vascular system. It functions by unilaterally returning lymphatic fluid to the vascular system where it is eliminated.
Almost every organ in the body has lymphatics which generate a variety of byproducts that require elimination. Examples of organs in the body that contain lymphatic tissue include the gastrointestinal (GI) tract, spleen, lymph nodes, tonsils, and thymus.
- Lymph nodes function to monitor the composition of lymphatic fluid/blood, engulf any pathogens, augment an immune response, and eradicate infection. They are like filtering stations for the lymph fluid.
- The thymus serves to mature and develop T cells in response to an inflammatory process, immune response or malignancy.
- The absorption and transport of fats and fat-soluble vitamins from the GI system also requires lymphatics.
- The lymphatic fluid is eventually emptied at the junction of the left subclavian vein and left internal jugular veins.
- Lymphatic fluid is derived from plasma. It leaks out of the capillary walls because of pressure exerted by the heart or osmotic pressure at the cellular level.
- In the GI tract, the lymphatic fluid has a milk-like appearance that is chiefly due to the presence of cholesterol, glycerol, fatty acids and other fat products. The vessels that transport the lymphatic fluid from the GI tract are known as lacteals.
- Lymphatic capillaries are very thin vessels which are blind-ended tubes. The lymphatic capillaries tend to form a large network of tubes that are known as lymphatic vessels.
- The key feature of lymphatic vessels is that they have thin endothelial walls and have an overlapping arrangement. This morphology allows for any fluid from the tissues to enter the cells. 
Diseases of the Lymphatic System
The lymphatic system is also prone to diseases like the venous and arterial circulation. Eg
- Lymphedema. When this occurs, the lymphatic system is unable to drain lymphatic fluid which results in accumulation of the fluid causing swelling of the extremity. Lymphedema is classified as primary or secondary.
- Primary lymphedema is an inherited disorder where the lymphatics may be missing or abnormally developed (eg. aplasia, hypoplasia, hyperplasia). This condition usually presents at birth or sometimes may present later in life.
- Secondary lymphedema is an acquired disorder that has a known cause such as cancer, infection, trauma or following a surgical procedure.
- Lymphomas are malignancies that arise from the cells of the lymphatic system. There is usually malignant transformation of specific lymphocytes in the lymphatics or lymph nodes that are present in the gastrointestinal tract, neck, axilla or groin. Symptoms of lymphoma may include night sweats, fever, fatigue, itching and weight loss.
- Cancers of a variety of organs may commonly spread to involve regional lymph nodes.
- Lymphadenitis occurs when the lymph nodes become inflamed. The cause is usually an adjacent bacterial infection. The lymph nodes usually enlarge and become tender.
- Filariasis is a very common disorder caused by a parasite in Africa. The parasite rapidly divided and obstructs the lymph nodes in the groin, making it difficult for the lymphatics to drain the extremity. This often results in huge extremities and marked disability.
Physiotherapy has a crucial part in helping to resolve problems with the lymphatic system such as using manual lymphatic drainage and exercise which are components of Complete Decongestive Therapy (CDT) ,,  . Exercise induces transport of lymph. Movement of muscles and arterial pulses cause the transport of lymph through the lymphatic system. Being active therefore has a positive effect of lymphatic system and the movement of lymph through our body. Some activities that are recommended are swimming, brisk walking, tennis, jumping, gymnastic, deep breathing, etc  
Manual lymph drainage has shown to be of benefit in examples below
- Hind foot operations:the application of lymph drainage techniques after hindfoot (the posterior part of the human foot that contains the calcaneus, talus, navicular, and cuboid bones) operations, in combination with standard physiotherapy exercises, achieves greater limb volume reduction than exercise alone. 
- Breast cancer related lymph edema: 
- Sports Medicine and Rehabilitation.
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